ibclogo XVI International Botanical Congess


Abstract Number: 4564
Session = 12.15.2


INTRA-TETRAD SELFING AND THE MAINTENANCE OF HETEROZYGOSITY IN THE SMUT FUNGUS


J. Antonovics and M. Hood. Dept. of Biology, U. of Virginia, Charlottesville, VA 22803


Anther smut fungus Microbotryum violaceum (=Ustilago violacea) has become an important model system for the study of host-parasite interactions in natural plant populations. Disease transmission occurs when pollinators carry spores to healthy plants. On germination, the diploid spores undergo meiosis and produce a yeast-like generation with cells of two mating types a1 and a2. Conjugation between opposite mating types is necessary for infection. Nevertheless, recessive mutations which lead to early death in the haploid stage are found at high frequencies in natural populations. The persistence of such lethal mutations is facilitated by a mating system which bypasses the haploid generation and involves intra-tetrad selfing among the immediate meiotic products. In M. violaceum, centromere linkage of mating type results in conjugation between cells separated at the first meiotic division. Such mating systems maintain heterozygosity in centromere regions of all chromosomes and not just around the mating type locus. Saturation mapping of tetrads indicates that a large proportion of the heterozygous loci in M. violaceum exhibit first division segregation.


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